Asthma is a common clinical condition that affects approximately 1% of all pregnancies and may result in significant morbidity for both the fetus and the mother. Asthma during pregnancy has been associated with low birth weight, both from prematurity and decreased intrauterine growth. Cigarette smoking and race are factors associated with both asthma and low birth weight and, hence, of potential importance in explaining the association of asthma or low levels of lung function with these adverse pregnancy outcomes. Roughly one third of asthmatic women get significantly worse during pregnancy and the reasons for this are unclear. Also, it is unknown whether asthma therapy influences utilization of health services and the clinical outcome of asthma in pregnancy. The specific aim of this proposal is to analyze data on a clinical cohort of pregnant asthmatic women and nonasthmatic controls (HCHP) and to analyze data already available from a case control study of airways responsiveness and preterm labor, and a prospective study of maternal smoking on infant lung function to determine the effect of maternal asthma on maternal and fetal pregnancy outcomes.